The heavy chain switch is a regulated DNA recombinational deletion that has important implications for protection against infectious agents. In the normal event in B lymphocytes, a deletion event begins in DNA sequences that lie upstream of the mu heavy chain constant region and ends in DNA sequences that lie upstream of the gamma, epsilon, or alpha constant region genes. This deletion event bring the exon encoding the variable region into juxtaposition with a new constant region, allowing B lymphocytes to express a new type of antibody that may be more suitable for a given pathogen. In rare instances, one of the heavy chain genes undergoes a recombination event with the c-myc oncogene on a different chromosome. This aberrant heavy chain switch, resulting in a reciprocal chromosomal translocation, is one of the underlying causes of plasmacytomas in mice and lymphomas in humans. Our long term goal is to understand the sequence requirements of both physiologic switch recombination and the aberrant switch recombination that leads to tumors. In order to study the regulation and mechanism of switch recombination, we have developed a 230 kb transgene of the entire heavy chain constant region locus that is able to undergo switch recombination like that of the endogenous heavy chain genes. In the feasibility project proposed here, we will determine if the transgenic heavy chain locus can also undergo chromosomal translocations to c-myc, resulting in plasmacytomas. In Aim 1 we will test for translocations, after induction of plasmacytomas with pristane, to the transgenic heavy chain genes of mice with three or four copies of the transgene. In Aims 2 and 3, we will test for translocations to the transgene with an induction protocol that includes co-expression of a bcl-xL transgene. We will correlate the ability of the heavy chain transgene to translocate with chromosomal insertion site, orientation, and allelic exclusion. If the heavy chain locus transgene can undergo translocations with c-myc, the ability to make any desired mutation, deletion, or insertion in the transgene provides us with an opportunity to determine which elements in the heavy chain locus are critical for the aberrant recombination event and subsequent deregulation of c-myc transcription. Relevance to mission of the Institutes: Information gained from these studies will improve our understanding of how the chromosomal translocations common in tumors occur. The information is also likely to be relevant to normal switch recombination, with implications for better vaccine design. [unreadable] [unreadable] [unreadable]